Suppose the circumference of a circle is ${10\pi}$. What is its area?
Explanation: ${c = 10\pi}$ ${K = 25\pi}$ First, find the radius: $r = c/2\pi = {10\pi}/2\pi = {5}$ Now find the area: $K = \pi r^2$, so $K = \pi \cdot {5}^2 = {25\pi}$.